Low-tension ignition spark plug for condenser discharge



5, 1952 w. B. sMn's 2,605,754

LOW-TENSION IGNITION SPARK PLUG FQR CONDENSER DISCHARGE Filed Sept. 21, 1948 s Sheets-Sheet 1 .Wyfze Beye Smits 1952 w. a. SMITS 2,605,754

LOW-TENSION IGNITION SPARK PLUG FOR CONDENSER DISCHARGE Filed Sept. 21, 1948 3 Sheets-Sheet 2 Wytze Beye Smifs W. B. SMITS Aug. 5, 1952 LOW-TENSION IGNITION SPARK PLUG FOR CONDENSER DISCHARGE Filed Sept. 21, 1948 5 Sheets-Sheet 3 Wytze Beye Smia;

Patented Aug. 5, 1952 UNITED STATES PATENT OFFICE LOW-TENSION IGNITION SPARK PLUG FOR CONDENSER DISCHARGE Wytze Beye Smits, Voorburg, Netherlands, assignor to Smitsvonk N. V., The Hague, N etherlands, a corporationof the Netherlands Application September 21, 1948, Serial No. 50,308

Inthe Netherlands October 4, 1947 The present invention relates to lowtension spark plugs with supported spark gap for condenser discharge.

Such spark plugs are known from the Dutch Patent No. 46,114, issued June 16, 1949. In this patent two, amongst others, of the fundamental requirements for a good operation of such spark plugs have been indicated, 1. e.: a supported spark gap narrower than 0.3 mm. and the non-combustion of the-carbon particles deposited upon the insulation separating the electrodes, and constituting the supported spark gap said particles promoting the spark discharge. In order to ensure a long useful'life of such low tension spark plugs, the electrode material and the attachment of the electrodes to the insulation should meet certain requirements. These re-.- quirements are connected, amongst others, with the fact, that, as such spark plugs operate at low tensions, higher currentintensities are to be used inorder to achieve the certainty of ignition. z

The object of the present invention is to prolong the useful life of the low tension spark plugs very considerably by giving the electrode members a suitable shape, on the one hand, and by connecting the electrode members tothe insulation disposed in between soas to. form an exchangeable solid electrode assembly, on the other hand. This permits the use of the spark plug body proper for a practically unlimited time, renovations being limited to the mere replacement of the electrode assembly. ,The exchange ableelectrode assemblies too are shaped so as to ensure along usefullife period.

Another object of the invention is to provide a low tension spark plug with a supported spark gap of great length to facilitate the formation of a carbon deposit thereupon.

A further object of the invention is to provide a low tension spark plug with a cool supported spark gap equally to facilitate the formation the carbon deposit thereupon.

According to the invention the spark plugmainly consists of a metallic spindle, suitably connected with the current source, which spindle is surrounded by a thin insulation layer, consisting, for example, of mica, porcelain, or any other suitable insulating material, embraced by a shell, which can be screwed into the wall of the explosion or combustion chamber. The exchangeable electrode assemblies can be fastened to the spark plug in a suitable manner and can easily be replaced by other ones. Preferably the shape of the electrode members is such, that the effective faces thereof, between which 20 Claims. (Cl. 12 3169) creep sparks are generated, are as long as possible, in other words the developed length of the surface of the electrode members, which surface constitutes the supported spark gap being so great thatthe surface'of the spark gap cannot be entirely swept by one spark. As already set out above the presence of a carbon deposit on the spark gap is desirable to facilitate the spark discharge. By making the length of the spark gap greater than the breadth of the spark while the spark burns off the carbon already deposited on its path, the carbon deposit on another part of the spark gap has the possibility of building itself up during the operation of the spark plug. When the resistance of the part along which the spark occurred has increased dueto the destruction of the carbon deposit and becomes greater than that of another portion of the spark gap upon which the carbon deposit, meanwhile, has been formed, the sparks will transfer themselves to this new portion of the spark gap; Afterthis has happened the first portion of the spark gap has the possibility of reconstituting a carbon layer while the carbon layer of the new spark path is destroyed by the occuring sparks. The action therefore is, in a way, a continuous cycle. Another advantage of long active faces of electrode members is a substantial increase of the active life of the electrode assembly. The breadth of the spark gap gradually increases through the wear of electrode members and when t exceeds a certain value, the electrode members in the usual spark plugs either have to be reset, or the spark plug must be replaced by a new one.

Due to the special form of the electrode members according to the present invention the spark gap increases only very slowly thereby considerably prolonging the useful life of the spark plug. The insulation resistance between the electrode members measured in a cold and clean state with low' tensions amounts suitably to 80,000 ohms or less.

The exchangeable electrode assembly is in contact, on the one hand, with the grounded external shell of the spark plug and, on the other hand, with the spindle insulated from the shell, said spindle being suitably connected with the current source. As the spindle of the spark plug has a greater diameter than the core electrode of the usual spark plug constructions, the heat concentration in the plane of contact between spindle and insulation is much lower than in the usual embodiments. This permits'the requirements, which the insulation as well as the fixation of the spindle in the insuinsulator separating the lation must meet, to be much lower than in the usual constructions, said requirements being for the insulator to provide sufficient electrical insulation and not to develop cracks, and for the fixation to be free from gas leaks and to provide a mechanically strong connection between the insulator and the spindle. The lower the temperature, the easier it is to meet these requirements, as the difliculties increase with higher temperature.

It is equally of advantage to provide good metallic contact over large areas between the electrode assembly and the spark plug body as well as with the fastening means securing said assembly to said body. This measure together with the large cross-sections of the spindle and the outer shell of the spark plug body greatly facilitates the heat transfer from the electrode assembly to the spark plug body and further, keeping the supported spark gap cool and facilitating the formation of a carbon deposit thereupon during the operation of the spark plug.

The material of the electrode members proper has to be a good conductor. Suitable materials are silver and copper. In order to prolong the life period of the electrode members it is of particular advantage to plate their spark producing surfaces with a non-oxidizing heat resistant metal. I am well aware of the fact that it is known to provide the electrodes with a protective covering of a precious metal. What I claim is a protective covering consisting of nonprecious metals, such as e. g. tungsten. It is equally possible to provide a thin layer of a nonoxidizing heat resistant material, such as, for example, tungsten, between the electrode members and the insulator.

The present invention will be further illustrated by means of the drawings showing some embodiments thereof. It should be mentioned, that the embodiments shown are only given by way of example.

In the accompanying drawings Figs. 1 and 2 show partly in longitudinal section and partly in elevation two difierent embodiments of the device according to the invention,

Figs. 3 and 4 show partly in elevation, partly in longitudinal section two other embodiments of the electrode assembly according to the invention,

Fig. 5 shows partly in elevation, partly in longitudinal section yet another embodiment of the invention,

Fig. 6 represents in top view the electrod assembly according to Fig. 5,

Figs. 7 and 8 show in top view two other embodiments of electrode assemblies of the same general arrangement as represented in Figs. 5 and 6.

In Fig. 1 there is shown a spindle I separated by the insulation layer 2 from the shell 3. One or more washer-shaped electrode bodies l are secured to the spark plug body, for example by means of a screw 6 or in any other suitable way. If more than one electrode assembly is applied. they are spaced, for example by means of a conductive metal ring (rings) 5, which may also form a whole with the electrode assemblies. An electrode assembly l consists of a fiat insulating ring to which along the inner and the outer circumferences electrode members 1 and 8 are fixed along the inner and outer circumferences of the ring, annular supported spark gaps 55 being provided between the electrode members. The gap l facing insulation 2 is kept sufficiently wide to prevent the occurrence of sparks. When using more than one electrode assembly the shell of the spark plug is provided with holes I2 in order to form a communication of the interior space 13 with the explosion or combustion chamber. The gap or gaps II) can be filled with gases or with insulating material to make it flush or nearly flush with the electrode members.

When a spark occurs it will take place across one of the spark gaps H), the place of the spark being. where the gap H] has the lowest resistance. The electrodes 8 are suitably connected to the current source and to each other, by means of the spindle I, the screw 6 and the rings 5, whereas the electrode members I are in contact with the shell 3 of the spark plug and thence with the ground.

The total length of the gap or gaps 10 being very great, the sparking increases the breadth of the spark gap only very slowly resulting in a long useful life period. When the gaps have become too wide, the electrode assemblies 4 can be replaced by new ones in an easy and rapid manner.

Fig. 2 shows another embodiment of the spark plug according to the present invention. M is the shell, separated, by means of the insulation layer l5, from the spindle IS. The electrode assembly 11 consists of a pile of flat electrode rings I 9 and 20, separated from each other by means of the insulating layers 2|. The electrode assembly I! is fixed to the spark plug body by any appropriate means, for example, by means of a screw I8. The screw l8, screwed into the spindle of the spark plug, connects suitably the upper electrode member source. The bottom electrode member 20 is directly pressed against the shell l of the spark plug and grounded. The electrode members of the same polarity (positive or negative) are interconnected by the conducting means 22, or 23, respectively. The spark occurs along the exterior circumference of the electrode assembly H, in any place between any two electrode members I9 and 20. The supported. spark gap corresponds to the thickness of the insulating layer 2|. By an adequate adaptation of the insulating material to the electrode material it is possible for the burning-in of the electrode and of the insulation to keep pace with one another. Eventually the insulation may burn in a little more than the electrode material. The burning-in of the insulation may be decelerated by giving the insulation layers 2| a thickness, which increases toward the center line of the spark plug, so that, when burning-in of the insulation has taken place, the surface of the insulation exposed to the flame action has become greater. This enables the electrodes now projecting to some extent to burn off more rapidly than the insulation, thereby restoring the original form. The same effect can be obtained by making the electrode thinner towards the interior.

Fig. 3 shows an embodiment of an electrode assembly which is in some respects similar to that represented in Fig. 2. The assembly comprises a plurality of stacked annular disk electrode members 39, and 24 insulated from each other by means of insulating layers 28, alternate electrode members being connected with each other by means of the tubular extension of the electrode member and the pins 29 respectively. Insulating rings 28 insulate the electrode members 25 from the tubular extension of the elec- IS with the current trode member 30, whereas the insulating rings 2] separate electrically the electrode members 24 from the pins 29. I The electrode assembly can be removably secured to a spark plug body of the type represented inFigs. 2 or 5, for example by means of a'screw similar to that represented in Fig. 5.

Fig. 4 shows another embodiment of an electrode assembly. It is constituted by a cylindrical body of insulating material 3|, the outer surface whereof is provided with a double threaded groove, wherein electrically conductive material is disposed to form helical shaped electrode members. In the embodiment shown wireshaped conductors 32, 33 are first located at the bottom of said grooves and electrically conductive material" is then molded into said grooves the wire-shaped conductors 32 and 33 may be omitted but I prefer the first described embodiment as it has a greater reliability.

The grooves may be given a rectangular, semicircular, triangular or any other suitable shape according to the desired rates of the burning-off of the insulating and the electrode material.

The Figs. 5, 6, '7 and 8 show another embodiment of the electrode assembly. 39 is the spindle of the spark plug, separated from the shell 40 by means of the insulating layer 4|. attaching means of the eelctrode assembly, consisting of the parts 35,. 36 and 31 fixed to one another. The electrode member is grounded via the shell 40 and shaped asa relatively thick disk, consisting, for example, of copper. 36 is a thin insulating layer. Theelectrode member 31 is connected via the attaching means 38 with the spindle of the spark plug. The electrode member 31 may consist either of a thin plate of metal, such as copper, for example, (Fig. 6) or of metal gauze (Fig. 7) or of perforated metal plate (Fig. 8), or may be formed in any other suitable way. The thickness of the electrode 31 and the thickness and composition I cally insulated relation within said body member,

an electrode assembly removably secured to said spindle member, said assemblyconsisting of a plurality of electrode members having opposing spark forming surfaces, alternate electrode members being electrically connected respectively to said body member and said spindle member, and solid insulating material positioned in the spark gaps between the opposing electrode members trode assembly is removably secured to said spindle member by a continuous joint of opposed 38 is the of the insulation layer 36 are so adjusted with regard to one another, that they burn off simultaneously and regularly. This ensures a high operational certitude and a long life period.

der, instead of making it flat. The electrodes It is also possible to give this embodiment of the r electrode assembly the shape of a hollow cylinform the two mantle faces of the cylinder separated by an equally cylindrical insulating layer.

I claim:

1. A low voltage spark plug comprising an elec- I trically conductive body member, an electrically conductive spindle member mounted in electrically insulated relation within said body member, an electrode assembly consisting of a plu-' rality of annular electrode members, said members having opposing spark forming surfaces,

alternate electrode members being electrically connected respectively to said body member and said spindle member, and solid insulating matefl rial positioned in the spark gaps between the opposingelectrode members to form a continuous spark supporting surface, the annular spark gap thus formed having a length greater than the breadth of the spark produced, said electrode assembly being removably secured to said surfaces to form a seal therebetween, thereby providing a substantially voidless connection therebetween. L 4. A low voltage spark plug comprising an electrically conductive body member, an electrically conductive spindle member mounted in electrically insulated relation within said body member, an annular electrode assembly removably secured to said spindle member, said electrode assembly comprising an annular, disk of insulating material having inner and outer spaced rings of conductive material thereonto trically conductive body member, an electrically conductive spindle member mounted in electrically insulated relation within said body member, a plurality of spaced annular electrode assemblies removably securedto said spindle member, each of said electrode assemblies comprising an annular disk of insulating material having inner and outer spaced rings of conductive material thereon to form electrode members, the inner ring being electrically connected to said spindle member and the outer ring being electrically" connected to said body member, the insulating surface between the opposing spaced rings being adapted to form a spark supporting surface for the deposition of carbon thereon. I

6. A low voltage spark plug comprising an electrically conductive body member, an electrically conductive spindle member mounted in electrically insulated relation within said body member, a plurality of spaced annular electrode assemblies removably secured to said spindle member within said body member, each of said electrode assem'- blies comprising an annular disk of insulating material having inner and outer spaced rings of conductive material thereon to formelectrode members, the inner ring being electrically con-" nected to said body member, a plurality of holes in said body member in the vicinity of the spaces between said spaced electrode assemblies to admit the passage of combustible gases to said spaces, the insulating surface between the opposing spaced rings bein adapted to form aspark sup;

7 porting surface for the 'deposition of carbon thereon. I.

'7. A low voltage spark .plug'. comprisingan electrically conductive body member, an "elec-" trically conductive spindle member mounted in electricallyinsulated relation within said body member, an electrode assembly removably secured to said spindle membensaid assembly consisting of a plurality of stacked annular disk electrode members insulated from each other to form opposing spark surfaces, alternate-elect'rode' members being electrically interconnected and connected respectively to said body member and saidspindle member, the solidinsulating material positione'din the spark gaps betweenthe opposing electrodes thus forming continuous spark supporting surfaces, the annular spark gap thus formed having a length greater than the breadth of the spark produced.

8. A low voltage spark plug comprising an electrically conductive body member, an electrically conductive spindle member mounted in an electrically insulated relation within said body member an electrode assembly removably se cured to the electrically conductive spindlemember of the spark plug and comprising a cylindrical body of insulating material, said body having a double threaded, grooved exterior surface, electrically conductive material disposed in each of thethreaded grooves on said bodyto form helical shaped annular spark electrode members separated by the spark supporting surface of solid insulating material, 'each of 'said helical rings of conductive material being adapted to be connected to opposite terminals of a voltage source. I 1

9. A low voltage spark'plug comprising an electrically conductive body member, electrically conductive spindle member mounted in an electrically insulated relation within said body member an electrode assembly'removably secured to the electrically conductive spindle member of the spark plug and comprising a cylindrical body of insulating material, said body having a double threaded, grooved exterior surface, elec= trically conductive material molded ineach of the threaded grooves on said body to form heli cal shaped annular spark gaps separated by the sparksupporting surface of solidinsulating material, each of said helical rings of conductive material being adapted to be connected to opposite terminals of a voltage source. I

10'. The invention as claimed in claim '7 where in the insulating material between the opposing electrode members increases in width toward the interior of the body member.

11. The invention as claimed in claim 8 Wherein the insulating material separating the spark gaps increases in width toward the interior of the body member. Y

12. The invention of claim 7 wherein the outermost one of said disk electrode members is comprised of thin apertured metal.

13. A low voltage spark plug comprising an electrically conductive body member, an elec= trically conductive spindle member mounted in electrically insulated relation within said body member, a plurality of annular electrode members carried by said body and having opposing spark formula surfaces, alternate electrode members being electrically connected respectively to said body member and said spindle memberfand solid insulating material positioned in the spark gaps between the opposing electrode members to form a continuous spark supportin surface 8. forthe deposition of carbon deposits so as to have a surface resistance of less than 80,000 ohms, the annular spark gap thus formed-having a length "greater than the breadth of the spark produced.

' 14. The invention of claim 1 wherein the spark producing surfaces of the electrode members have a'plating of non-oxidising heat resistant material.

15; A low voltage spark plug comprising an electrically conductive body member, an electrically conductive spindle member mounted in electrically insulated relation within said body member, an electrode assembly removably secured to the electrically conductive spindle member of the spark plug and comprising a cylindrical body of insulating material, said body having a double threaded, grooved exterior surface, Wire'- shaped conductors located at the bottom of each of the threaded grooves on said body and molded electrically conductive material filling said grooves flush'with the cylindrical surface of said supporting surface, the annular spark gap thus formed having a length greater than the breadth of the spark produced.

' '17. An annular electrode assembly comprising an annular disk of insulating material having inner and outer spaced rings of conductive material thereon to form electrode members, the insulating surface between the opposing spaced rings being adapted to form a spark supporting surface for the deposition of carbon thereon.

13. An electrode assembly consisting of a plurality of stacked annular disk electrode members insulated from each other to form opposing spark surfaces, the'alternate electrode members being electrically interconnected, the solid insulating material positioned in'the spark gaps between the opposing electrode members forming continuous spark supporting surfaces, the annular spark gap thus formed having a length greater than the breadth of the spark produced.

19. Electrode assembly comprising a cylindrical body of insulating material, said body having a'double threaded, grooved exterior surface, electrically conductive material disposed in'each of'the threaded grooves on said body to form helical shaped annular electrode members, separated by the spark supportingsurface of solid insulating material.

- 20. An electrode assembly comprising a cylindrical body of insulating material, saidbody having a double threaded, grooved exterior surface,

\VYTZE BEYE SMITS.

(References on following page) REFERENCES CITED Number The following references are of record in the 11531203 file of this patent: ,0 e.

UNITED STATES PATENTS 5 Number Name Date 1,009,867 Terry Nov. 28, 1911 Number 1,445,712 Reijnhout Feb. 20, 1923 536,460

Name Date Von Lepel May 12, 1925 Berger Feb. 19, 1935 Anderson Oct. 15, 1935 FOREIGN PATENTS Country Date Great Britain May 15, 1941 

